The long range goal of this proposal is to better understand mechanisms regulating renal hemodynamics and glomerular function by hormonal paracrine and autacoid agents in health and disease. This proposal continues a focus on mechanisms of vascular reactivity and receptor signaling pathways in the renal microcirculation during development of genetic hypertension. A unique combination of coordinated studies of overlapping themes is designed to gain insight into regulatory mechanisms responsible for excessive renal vasoconstriction and increased tubulo-glomerular feedback activity in the spontaneously hypertensive rat (SHR). This proposal builds on the previous in vivo observations by the principal investigator, suggesting exaggerated renal vascular reactivity to angiotensin II (AII) in SHR which is primarily due to defective buffering afforded by vasodilator agents triggering the cAMP pathway. The primary abnormality in cAMP in SHR appears to be localized to the receptor-Gs-protein coupling. The enhanced renal vasoconstrictor response to vasopressin (AVP) also seen in SHR appears to be due to increased activity of the V1 AVP receptor. This proposal will continue to evaluate the central hypothesis that exaggerated renal vasoconstriction is mediated by direct actions of the vasoconstrictor agents on vascular smooth muscle cells either alone or in combination with a deficiency in the buffering capacity of the cAMP pathway. Proposed studies will conduct in depth investigation of the underlying mechanism using both intact animal and in vitro cells studies. The specific aims are: 1) To define the actions of AII on renal resistance vessels in genetic hypertension 2) To determine the effects of vasopressin on renal resistance vessels in genetic hypertension and 3) To investigate interactions of cAMP pathways and the vasoconstriction produced by AII or AVP in renal resistance vessels in genetic hypertension. Studies will involve whole kidney and single nephron in vivo studies, as well as in vitro work on freshly isolated tissue and cultured cells to evaluate second messenger signal transduction. Key steps will be assessed such as receptor expression and coupling with G proteins, phospho lipase C stimulation, IP3 generation, calcium channel activation and calcium store mobilization, and protein Kinase C activation. This search for significant abnormalities in vascular actions should provide new information providing a more complete understanding of normal regulatory mechanisms as well as defects in control systems that may cause or contribute to the development of genetic hypertension.